How do I drive two Dell M110 projectors from my new 15" Macbook pro

I am trying to drive two Dell M110 projectors from my 15" Macbook Pro. When connecting one projector via the HDMI port I am able to utilize two seperate "screens" (laptop screen and projector display), but when I connect any projectors via the Thunderbolt port I am only able to clone the laptop desktop across all the connected displays. I want to be able to display a seperate image on each display. I am running Mountain Lion 10.8.2 and Windows 7 via Parallels 8. Thank you.